Sugar oxidoreductases and veratryl alcohol oxidase as related to lignin degradation

Properties of cellobiose:quinone oxidoreductase (CBQ), cellobiose dehydrogenase (CDH), glyoxal oxidase (GLOX), glucose oxidases and veratryl alcohol oxidase (VAO) are reviewed. There is strong evidence that CDH reduces quinones, phenoxy and cation radicals. Glucose oxidases (glucose 1-oxidase and pyranose 2-oxidase) and VAO have been less investigated but evidence for reduction of the above compounds is accumulating. Pyranose oxidase, glyoxal oxidase and VAO are very important for hydrogen peroxide production by white-rot fungi. CDH is only produced on cellulose or on wood, whereas pyranose oxidase and VAO are produced both on wood and on rich glucose media suggesting that the lignin degrading white-rot fungi may use different quinone and radical reducing enzymes to regulate lignin polymerization/depolymerization depending on the substrate and cultivation conditions. Intracellular quinone reductases are also produced. Whether brown-rot fungi in general produce CBQ/CDH or VAO is not clear. The Fe(III) reducing ability of both CDH and certain phenolate compounds agree with the rapid depolymerization of cellulose by brown-rot fungi. The interaction of Fe(III) reduction with the hydrogen peroxide producing system in white-rot and brown-rot fungi requires more investigation. (C) 1997 Elsevier Science B.V.